A FINEX method, a coal-based molten iron making method, includes a fluidized reduction process for reducing fine iron ore, an agglomeration process for agglomerating the reduced fine iron ore, and a melting furnace process for melting the agglomerated and reduced iron ore in a melting furnace including a coal filling layer. Certain amounts of by-products are discharged from each of the processes.
The by-products include large amounts of materials usable in a molten iron making process, such as iron ore, supplementary materials, and carbon-containing materials, and it is economically desirable to recycle the by-products in a molten iron making process. The by-products may be collected in the form of sludge by using water or in the form of dust without using water.
However, it is not easy to handle by-products collected in the form of sludge because of moisture contained in the by-products, and a pretreatment process is necessary before recycling the by-products. That is, it is necessary to remove moisture from sludge-type by-products to some degree before recycling the sludge-type by-products, and this requires a large amount of energy.
In addition, since such by-products have a significantly small particle size, on the level of 100 μm or less, if the by-products are directly used in a molten iron making process, most of the by-products may be blown off. Therefore, because of such problems, by-products are agglomerated and then recycled in a melting furnace process.
When by-products are recycled in a melting furnace process, dust-type by-products are agglomerated and then inserted into a melting furnace, and sludge-type by-products are dried, agglomerated, and then inserted into a melting furnace. However, since agglomerated by-products have a low degree of room-temperature strength and a low degree of high-temperature strength (hot strength), the agglomerated by-products are easily broken during transfer or at the moment the agglomerated by-products are inserted into a melting furnace having a temperature of about 1,000° C. Particles broken from the agglomerated by-products may be blown by a reducing gas of the melting furnace and may be discharged in the form of dust or sludge, thereby decreasing the efficiency of recycling. In addition, if particles broken from the agglomerated by-products remain in the melting furnace, the particles may fill pores of large particles, and thus the permeability of the large particles may be decreased.
To address these problems, binders are used to improve the coupling strength of particles, or a high-temperature heat treatment is performed as in a pelletizing process. In this case, however, energy consumption and manufacturing costs are increased, and the effects of recycling are lowered.
Because of the above-mentioned problems, by-products are limitedly reused in molten iron making FINEX systems, and thus most collected by-products are provided to cement plants requiring iron sources free of charge or are buried underground. Therefore, technology for recycling by-products using a minimum amount of energy while preventing breakage of agglomerated by-products is required.